Detection of blood leakage by detecting a volatile agent

ABSTRACT

A method of detecting bleeding from a wound including: providing, on a support, a substantially non-volatile agent capable of forming a volatile agent on contact with blood; disposing the non-volatile agent on the support at or near the wound; providing a probe for detection of the volatile agent; disposing the probe for detection of the volatile agent at a distance from the support; generating a flow of air in a direction from the support to the probe; monitoring the formation of volatile agent by the probe, thereby detecting a bleeding of the wound. Also disclosed are a system and a disposable device for use in the method.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the U.S. national phase of PCT Application No.PCT/SE2011/000197 filed on Oct. 31, 2011, which claims priority toSwedish Patent Application No. 1001065-0 filed on Oct. 29, 2010, thedisclosures of which are incorporated in their entirety by referenceherein.

FIELD OF THE INVENTION

The present invention relates to a method and a system for detectingblood leakage from a wound.

BACKGROUND OF THE INVENTION

A well-recognized problem in hospital care is that wounds caused bysurgery or accidents, in spite of having been properly closed anddressed, may start to bleed again. Due to the dressing by which thewound is covered or due to the patient being unconscious or otherwiseunable to recognize the bleeding, it is only noticed by the staff andtaken care of after a while. In the meantime the patient may have lost asubstantial volume of blood. This will no doubt have a detrimentaleffect on his or her recovery.

Another problem of similar kind is quite frequently seen in blooddialysis. In a life saving treatment patients with impaired ornon-existing renal function purify their blood from salts, urea andother metabolic degradation products on a regular basis, such as two orthree times per week. In blood dialysis an artery is punctured by acannula or needle to make a portion of the patient's blood pass througha dialysis apparatus in which it is purified. The purified blood isreturned to the patient by venous infusion through a cannula insertedinto a large vein. Most often arterio-venous fistula (or a correspondinggraft) is created at a patient's wrist or upper arm, from which blood isremoved by an arterial cannula and returned downstream by a venouscannula.

A cannula of this kind usually comes with wings extending from a shortcylindrical plastic tube in which the cannula is mounted. These wingscan be used for securing the cannula by adhesive tape to prevent it fromlongitudinal displacement in the vein, fistula, or graft. The adhesivetape may accidentally come off and the cannula withdrawn. Inevitablythis results in immediate bleeding, which may be quite severe. If thebleeding is not noticed and stopped at once the patient may lose a largevolume of blood. Since dialysis patients are usually anaemic, they areparticularly affected by such a loss. In addition it is important toprevent blood contained in the dialysis apparatus from being lost if acannula is removed accidentally. To cope with a loosening arterialneedle a safety means is included in known dialysis apparatus. Thesafety means comprises a pressure sensor disposed on the input side ofthe apparatus. If the sensor detects a sudden drop in pressure duringdialysis the flow of blood through the apparatus is immediately stoppedand the personnel alarmed. Due to the pressure drop in the venous needlea loosening thereof cannot be monitored easily in a correspondingmanner.

WO 06/001759 A1 discloses a method for detecting blood leakage from awound in which a sharp bend of an optical fiber is disposed at thewound. Light passing through the fiber is detected at one end of thefiber. Leaking blood contacting the fiber attenuates the passing light.The attenuation, which indicates blood leakage, is detected and an alarmis triggered. The method of WO 06/001759 A1 employs a device comprisingan optical fiber and a medical patch. For hygienic reasons the device isdisposable.

The provision of alternative methods of detecting blood leakage from awound not employing a disposable device or a disposable device, which ismore economical and/or simpler to manufacture than the prior art deviceis desirable.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a method and a system of theaforementioned kind, which is safe.

It is another object of the invention to provide a method and a systemof the aforementioned kind, of which a disposable device is moreeconomical to manufacture than devices known in the art.

Further objects of the invention will become evident from the followingsummary of the invention, the description of preferred embodimentsthereof illustrated in a drawing, and the appended claims.

SUMMARY OF THE INVENTION

The invention will be explained by reference to a wound caused byinsertion of a cannula into a vein. The teaching of the invention ishowever equally applicable to other kinds of wounds, both surgically andaccidentally caused wounds, that have stopped bleeding but are at riskof re-opening and bleeding.

The present invention is based on the insight that detection of avolatile agent formed by leaking blood contacting a substantiallynon-volatile agent can be used for this purpose.

More specifically, the present invention is based on the insight that avolatile agent can be formed by the reaction of blood with an agent oflow volatility, in the following called non-volatile agent, and that theformation of the volatile agent can be detected by a detection meansdisposed at a distance from the site of formation. The volatile agent isformed by reaction of the water component of blood with the non-volatileagent. In this invention, the non-volatile agent is an agent capable offorming a volatile agent from which it differs in boiling point by atleast 100° C., and even by 200° C. or 300° C. or more. The property oflow volatility of the non-volatile agent is important, since evaporationof the agent, at least of a substantial amount of it, should be avoidedduring the monitoring period to avoid compromising monitoring safety. Inrespect of hemodialysis a monitoring period is, for instance, 5 hours or7 hours. The amount of non-volatile agent evaporated during themonitoring period should not exceed 20%, preferably it should be lessthan 10%, most preferred less than 1%.

The volatile agent is transported by diffusion/convection to thedetection means. Preferably it is transported to the detection means bycontrolled convection. Controlled convection is convection controlled ina manner so as to create an air stream from the site of formation of thevolatile agent to the site of detection can be produced by a convectionproducing means. The air stream carries transports the volatile agentfrom the site of formation to the site of detection. A suitableconvection producing means comprises a fan, in particular anelectrically driven fan. The convection producing means of the inventionmay also comprise an air stream conducting means such as a tube disposedintermediate between the site of formation and the site of detection.

The volatile agent can be any agent capable of being transported by anair stream in a gaseous state except for a component of air comprised byoxygen, nitrogen, carbon dioxide, carbon monoxide, water, helium, andargon. While air does additionally contain a great number of othercomponents in amounts varying in respect of the particular environment,such as nitrogen oxides, hydrogen, and methane, their low concentrationcan be compensated for by setting an appropriate lower concentrationlimit for detection.

The non-volatile agent is disposed at a wound, such as a wound caused bythe insertion of a cannula into a blood vessel, so that it is contactedby blood leaking from the wound within a short period of time upon theonset of leakage, such a within less than 30 seconds and even withinless than 10 or 5 seconds. A volatile agent so produced can be detectedby a detector sensitive to the agent but essentially insensitive to acomponent of air or to the volatile agent below a selected detectionlimit.

Examples of suitable non-volatile agents of the invention are(respective volatile agent formed by contact with an aqueous media suchas blood in parenthesis):

CaC₂ (acetylene);

CaH₂ (hydrogen):

BaH₂ (hydrogen);

NaBH₄ (hydrogen);

KBH₄ (hydrogen);

NaBH₄ or KBH₄+catalyst, such as a carboxylic acid, CoCl₂, aluminum oxide(hydrogen);

NH₃BH₃+catalyst, such as Pd²⁺ or cation exchange resin, such asamberlite (hydrogen)

(NH₄)₂CO₃ (ammonia);

NH₄Cl+base, for instance Na₂CO₃ (ammonia); (NH₄)₂SO₄+base, for instanceNa₂CO₃ (ammonia)

a mixed anhydride of an ion exchange resin with carboxylic groups and alow-molecular carboxylic acid, in particular acetic acid (low molecularcarboxylic acid);

triethyl carbonate+acid, for instance citric acid (ethanol);

tripropyl carbonate+acid, for instance citric acid (propanol);

Na₂S+acid, for instance NaH₂PO₄ (hydrogen sulfide).

The non-volatile agent or a matrix comprising the non-volatile agent isattached to a support, in particular a textile woven or non-wovensupport, such as a cotton pad, a cellulose fiber pad, a syntheticpolymer fiber pad, including a pad comprising two or more fibermaterials. The pad is attached to the skin at the wound, that is,preferably not in contact with the wound but disposed in its immediatevicinity, such as surrounding the wound fully or partially. Attachmentof the pad to the skin can be by, for instance, a medical-gradeadhesive.

The catalyst or acid or base can be applied to the support in a mannerso as to keep it separate from the non-volatile agent until the supportis contacted by blood. An appropriate support is a layered supportcomprising one or more layers of non-volatile agent and one or morelayers of catalyst or base. A layer comprising any of non-volatileagent, catalyst, acid, and base can be protected by disposing it betweenempty layers.

Alternatively or additionally, the non-volatile agent can be entrappedin a matrix, such as a carbohydrate matrix, or enclosed in a shellreadily dissolvable in water, such as a shell of gelatin.

Gas detectors suitable for detection of the volatile agent of theinvention are known in the art. Particularly useful are semiconductorbased detectors comprising surfaces capable of selective adsorption ofthe volatile agent.

The invention will now be explained in more detail by reference topreferred embodiments thereof illustrated in a drawing.

SHORT DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic top view of the system of the invention mounted ata person's anterior forearm region, partially sectioned;

FIGS. 2-5 are radially sectioned views of a layered support loaded withthe substantially non-volatile agent of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

By means of a strap 14 provided with a Velcro® closure (not shown)extending around a patient's forearm the system of the invention shownin FIG. 1 is mounted at the anterior forearm region 1 for detection of aleakage of blood from a wound 4 caused by the insertion of a cannula 3into a vein 2, such as at an arterial-venous anastomosis. The cannula 3is connected with a dialyzer (not shown) by means of a flexible tube 6.A layered support 5 loaded with non-volatile agent of the invention isdisposed centered above the wound 4. The circular support 5 comprises atop face and a bottom face. The circumference of the bottom face isprovided with a medical adhesive by which the support 5 is attached tothe skin. The air intake opening of an air stream conducting tube 7 isdisposed at a short distance from the support 5 in a cranial direction.A gas detection probe 8 extends into the lumen of the tube 7 near theoutput opening thereof. The gas detection probe 8 pertains to a gasdetector 9 disposed between a casing 10 enclosing a cranial terminalportion of the tube 7 and said terminal portion. The gas detection probe8 is selectively sensitive to a volatile agent other than a naturalcomponent of air (nitrogen, oxygen, carbon dioxide, helium, neon, argon,xenon). When contacted by an agent to which it is sensitive, the probeemits or increases or decreases an electrical signal, which is receivedand analyzed by the gas detector 9. While trace amounts of hydrogen,hydrogen sulfide, and ammonia can be present in air, their presence isdisregarded from or compensated for in the present context. The gasdetector 9 comprises a microprocessor and software dedicated to theanalysis of the gas detection probe 8 signal. The gas detector 9including the probe 8 is powered by a battery 12, such as a rechargeablelithium ion battery. Proximally of the probe 8 a fan 13 powered by a DCmotor is mounted in the lumen of the tube 7. The fan 13 creates acranially directed air stream A in the tube 7. Air is sucked in at theair intake opening and expelled at the air output opening after the airstream has passed the gas detection probe 8. A volatile agent releasedat or from the support 5 will be sucked into the caudal opening of thetube 7 by the air stream generated by the fan 13 and made pass the gasdetection probe 8. If the volatile agent is one that has affinity to thegas detection probe 8, that is, is selectively adsorbed by a surface ofthe probe 8, an electrical signal of the probe 8 is created or amplifiedor attenuated. The signal or change in signal strength is detected bythe detector 9. If the signal or change in signal strength exceeds apreset limit, an alarm produced by an alarm unit 11 is triggered. Thealarm may be of a visual and/or audible nature. The visual or audiblealarm can be emitted by the alarm unit 11. Alternatively oradditionally, the alarm unit 11 can comprise a sender for transmissionof a wireless signal to a receiver (not shown) comprising visual and/oraudible alarm generating means like a flashing light or a bell orsimilar. The alarm signal can also be transmitted to a control room fromwhere one or several persons are supervising dialysis patients duringdialysis. Alternatively or additionally, the alarm unit 11 can beelectrically connected with the dialysis machine (not shown) to whichthe patient is coupled via one or two cannulae, only one cannula beingshown in FIG. 1. This connection allows to stop dialysis as soon as thealarm is triggered.

FIGS. 2 to 5 show supports according to the invention in radial section.Their circular bottom face is provided with a peripheral layer ofmedical adhesive 21, 31, 41, 51 and so defined. The layers are numberedstarting from the bottom layer.

The support 20 of FIG. 2 comprises three layers of non-woven cottonbonded by a polymer melt applied at intersections of a square netpattern. Layers 22 and 24 are empty protective layers. The intermediatelayer 23 comprises calcium hydride flakes of a minimum sieved size so asto be firmly held by the cotton threads. Blood reaching the intermediatelayer via bottom layer 22 reacts with calcium hydride under formation ofhydrogen, which can be detected by a hydrogen-specific gas detectionprobe.

The support 30 of FIG. 3 comprises a bottom layer 32 and a top layer 34layers of non-woven cotton interspaced by a central layer 32 ofcellulose acetate fiber. The central layer comprises calcium carbidemade adherent to the fibers by contacting it with a solution ofpolyvinyl chloride-vinyl acetate copolymer dissolved in tetrahydrofuran.

Blood reaching the intermediate layer 33 via the bottom layer 32 reactswith calcium carbide under formation of acetylene, which can be detectedby an acetylene-specific gas detection probe.

The support 40 of FIG. 4 comprises a bottom layer 42 and a top layer 45of non-woven cotton interspaced by two layers 43, 44 of same material.Layer 43 comprises citric acid and heparin made to adhere to the fiberby aqueous carboxymethyl cellulose. Layer 44 comprises sodiumborohydride deposed on the fiber as from a solution in diglyme. Thelayers are not bonded; they are kept in the illustrated layeredconfiguration by encasement in form of a net of polypropylene fibers(not shown). Blood reaching the citric acid layer 43 via the bottomlayer 42 dissolves the citric acid, the aqueous solution of which istransported to adjacent layer 44 where sodium borohydride is dissolvedand reacted with water under formation of hydrogen, which can bedetected by a hydrogen-specific gas detection probe.

The support of FIG. 5 comprises a bottom layer 52 and a top layer 57 ofa cotton web. The layer 53 abutting the bottom layer is of fluffynon-woven cotton soaked with an aqueous solution of NaH₂PO₄ and heparin,then thoroughly dried. The layer 54 on top of the sodium dihydrogenphosphate layer 53 is of an empty cotton web. The layer 55 disposed ontop of the layer 54 is of fluffy non-woven cotton soaked with an aqueoussolution of sodium sulfide and then thoroughly dried. Blood enteringfrom below the bottom layer 52 and from there the sodium dihydrogenphosphate layer dissolves NaH₂PO₄ under formation of an acidic aqueoussolution which, after passage through the empty separating layer 54enters the sodium sulfide layer 56 and dissolves sodium sulfide which isdecomposed in the acidic media to hydrogen sulfide and disodium hydrogenphosphate. Hydrogen sulfide evolves as a gas from the solution and canbe detected by a hydrogen sulfide-specific gas detection probe.

The invention claimed is:
 1. A method of detecting bleeding from awound, comprising: providing, on a support, a substantially non-volatileagent capable of forming a gaseous volatile agent given off to thesurrounding air on contact with blood; disposing the non-volatile agenton the support at or near the wound; providing a probe for detection ofthe volatile agent from the air surrounding the support; disposing theprobe for detection of the volatile agent at a distance from thesupport; generating a flow of air in a direction from the support to theprobe; and monitoring the formation of said volatile agent with theprobe, to thereby detect bleeding of the wound.
 2. The method of claim1, wherein the non-volatile agent is calcium hydride, barium hydride,calcium carbide, borohydride, sodium sulfide, ammonium salt, orthoester,NH₃BH₃, mixed anhydride of ion exchange resin with carboxylic groups orlow-molecular carboxylic acid.
 3. The method of claim 2 wherein thenon-volatile agent comprises sodium borohydride or potassiumborohydride.
 4. The method of claim 2 wherein the non-volatile agentcomprises an ammonium salt selected from the group of ammoniumcarbonate, ammonium sulfate, and ammonium chloride.
 5. The method ofclaim 1, further comprising providing an acid, a base, or a catalystadjacent to said non-volatile agent, said acid, base or catalystpromoting generation of said volatile agent by said non-volatile agentwhen in contact with blood, thereby enhancing generation of saidvolatile agent.
 6. The method of claim 5, wherein a base providedadjacent to said non-volatile agent, the base being selected from agroup consisting of alkali carbonate, alkali hydroxide, dialkaliphosphate, trialkali phosphate, and calcium hydroxide.
 7. The method ofclaim 1, wherein the flow of air is generated by a fan.
 8. The method ofclaim 1, wherein the probe is a semiconductor probe.
 9. The method ofclaim 1, wherein the volatile agent is selected from a group consistingof hydrogen, acetylene, methanol, ethanol, hydrogen sulfide, ammonia,and C₁-C₃ carboxylic acid.
 10. A system for detecting bleeding from awound, comprising: a substantially non-volatile agent arranged on asupport, the non-volatile agent being capable of forming a gaseousvolatile agent which is given off to the surrounding air on contact withblood; a probe for detection of the volatile agent; a flow generatorgenerating a flow of air from the support to said probe.
 11. The systemof claim 10, wherein the flow generator is an electrically driven fan.12. The system of claim 10, comprising a guide, directing the flow ofair in a selected direction.
 13. The system of claim 12, wherein theguide comprises a tube.
 14. The system of claim 10, wherein thenon-volatile agent is selected from a group consisting of: calciumhydride, barium hydride, calcium carbide, borohydride, sodium sulfide,ammonium salt, orthoester, NH₃BH₃, mixed anhydride of ion exchange resinwith carboxylic groups, and low-molecular carboxylic acid.
 15. Thesystem of claim 10, wherein the support is layered.
 16. The system ofclaim 10, further comprising at least one of an acid, a base and acatalyst arranged on a layer of the support adjacent to another layersupporting said non-volatile agent.